1. Field of the Invention
Present invention is used for a disc reading apparatus such as an optical disc apparatus or the like, and relates to a disc reading control apparatus for controlling the rotational speed of a disc recording medium.
2. Description of the Related Art
FIG. 4 is a block diagram showing a conventional disc reading apparatus, which will be described below with reference to this figure.
The conventional disc reading apparatus comprises a disc 1 as a disc recording medium; a read head 2 opposed to the recording surface of the disc 1 for getting information from that recording surface; a signal processing unit 3 for processing a read signal outputted from the read head 2 to read data; a microcomputer 4xe2x80x2for outputting a setting information, such as a reading speed, a rotational speed or the like, based on the read data, while determining the position of the read head 2 to output a setting information for shifting the read head 2 to the next read position; a servo controller 5 for outputting, based on the setting information from the microcomputer 4xe2x80x2, control signals for controlling the rotation of the disc 1 and the shift of the read head 2; a spindle motor 6 controlled in rotation by an output from the servo controller 5 for providing the rotation of the disc 1; and a thread motor 7 controlled in shift by an output from the servo controller 5 for shifting the read head 2. For example, the disc 1 is an optical disc, while the read head 2 is an optical head.
The operation of the conventional disc reading apparatus during a disc reading will now be described below.
At first, during the disc reading, the microcomputer 4xe2x80x2 causes the servo controller 5 to set the rotational speed to its maximum. At this moment, the disc 1 rotates at an upper limit of the rotational speed, and the read head 2 reads information from the recording surface of the disc 1 and applies the read information to the signal processing unit 3. The data processed by the signal processing unit 3 is inputted to the microcomputer 4xe2x80x2.
Subsequently, the microcomputer 4xe2x80x2 decides, on the basis of the thus read data, whether or not a searching operation is necessary so as to get a next data. If the searching operation is necessary, the microcomputer 4xe2x80x2 sets the servo controller 5 to the searching operation, which shifts the read head 2. Since no data can be got during the shift of the read head 2, the data getting from the read head 2 through the signal processing unit 3 is resumed after the termination of the shift of the read head 2.
As can be seen from the above, the conventional disc reading apparatus performs the data getting and searching operations with the maximum speed having been set.
As long as a difficult situation, such as a reading difficulty, does not occur, the conventional disc reading apparatus does not change the rotational speed of the disc recording medium during the reading operation. However, as the reading speed has been more enhanced in recent years, there has been less time to effect a pull-in of a servo control when the shift of the read head during the searching operation or the like frequently occurs. As a result, the disc reading temporarily cannot be performed, or at the worst, the servo control is lost.
It is an object of the present invention to provide a disc reading control apparatus and method that can effect a stable searching operation with no degradation of the reading capability, while realizing an enhancement of the disc reading speed or of the rotational speed, by use of a relatively simple structure.
A disc reading control apparatus according to the present invention comprises operation information inputting means for inputting information concerning data getting and searching operations in a data reading operation with respect to a disc recording medium; operation ratio determining means for determining the ratio of the searching operation to the data getting operation on the basis of the information inputted from the operation information inputting means; and rotational speed setting means for setting the rotational speed of the disc recording medium lower if the foregoing ratio of the searching operation determined by the operation ratio determining means is greater than a predetermined value. A disc reading control method according to the present invention is used for the disc reading control apparatus according to the present invention.
A large ratio of the searching operation to the data getting operation during the reading operation means that the shift of the read head frequently occurs. If this condition is left as it is, it results in no sufficient time being left to perform a pull-in of the servo control after shifting the read head. Then, it is proposed that the rotational speed of the disc recording medium be set lower so as to perform a stable servo control after shifting the read head. It should be appreciated that in this application, the meaning of a phrase, xe2x80x9cif the ratio of the searching operation to the data getting operation is greater than a predetermined value, the rotational speed of the disc recording medium is set lowerxe2x80x9d, is equal to the meaning of a phrase, xe2x80x9cif the ratio of the searching operation to the data getting operation is smaller than a predetermined value, the rotational speed of the disc recording medium is set higherxe2x80x9d.
Besides, there may be additionally provided rotational speed limiting means for placing upper and lower limits on the rotational speed set by the rotational speed setting means. The operation information inputting means may input, as the information concerning the data getting and searching operations, the number of times of or the time period of the data getting operation and the number of times of or the time period of the searching operation. Moreover, as the foregoing ratio of the searching operation determined by the operation ratio determining means becomes greater, the rotational speed setting means may set the rotational speed of the disc recording medium variably or stepwise lower. Furthermore, the rotational speed setting means may set the rotational speed gradually lower.
In other words, the present invention is characterized in that when the searching operation frequently occurs during the disc reading, the rotational speed of the disc is variably or stepwise reduced. That is, the percentage of occurrence of the searching operation within a time period during the disc reading is determined, and if the determined percentage of the searching operation is large, the rotational speed is gradually reduced to a predetermined value; if the determined percentage of the searching operation is small, the rotational speed is gradually raised to a predetermined value. In this way, the reading speed is kept high during a continuous reading, while, when the searching operation frequently occurs, the rotational speed is reduced to such a degree that there is a sufficient time to perform a servo pull-in, thereby realizing a stable disc reading.